QuickLinks
 -- Click here to rapidly navigate through this document











 



 
 

Exhibit 10.21    
    


RIO TINTO AMERICA  


Kennecott
Energy & Coal

505 South Gillette Avenue

Gillette Wyoming 8271-3009

USA 


24 June
1998 


Dear
Sirs 


Facility of up to $800,000,000 with effect from 1 July 1998



We
write to offer to make available to you a new credit facility of up to $800,000,000 at anytime outstanding on the following terms: 



	a)
	this
facility will replace the existing $150,000,000 facility between the two companies.



	b)
	you
should give us written notice that you require funds not less than one day before the funds are required. Each written notice should specify the amount to be borrowed, the day upon
which the funds are to be made available, and the account into which the funds should be paid.



	c)
	interest
on borrowings will be paid by you on a quarterly basis as agreed between ourselves. Interest will be calculated on the daily average borrowings outstanding during the quarter
at a rate equal to our average commercial paper borrowing costs, plus a margin of point three zero per cent (0.30%).



	d)
	borrowings
can be repaid in whole or in part on such date or dates as may be agreed between us. Any amounts repaid will be available for redrawing. 




Please
signify your acceptance of the terms contained in this letter by signing and returning to us the enclosed copy of this letter. 


Yours
faithfully

Rio Tinto America Inc. 



	/s/ SIGNATURE ILLEGIBLE
 Director/Officer	 	 
	
Agreed & Accepted:	
 	

 
	

[SIGNATURE ILLEGIBLE]
 Signature	
 	

June 29, 1998
 Date
	

President & CEO
 Title	
 	

 





















  Rio Tinto America Inc.
  100 Quentin Roosevelt Boulevard

Suite 503

Garden City

New York 11530

United States of America 


14 June
1999



Kennecott
Energy & Coal Company

505 South Gillette Avenue

Gillette

Wyoming 8271-3009

U.S.A. 


Dear
Sirs, 


Facility of up to $800,000,000 with effect from 1 July 1998  


We
refer to the letter agreement dated 24 June 1998 between you and us whereby we agreed to make available to you a credit facility of up to $800,000,000 at any time outstanding on the terms
set out therein (the "Letter Agreement"). 


Following
our recent discussions, you and we have agreed that the rate of interest payable on borrowings under the credit facility shall be changed. With effect from 1 April 1999, the words "a
margin of point three zero per cent (0.30%)" in paragraph 1 (c) of the Letter Agreement shall be deleted and the words "a margin of two point one zero per cent (2.10%)" substituted
therefor. The Letter Agreement shall continue in full force and effect amended, with effect from 1 April 1999, as set out above. 


This
letter shall be governed and construed in accordance with the laws of the State of New York. 



We
would be grateful if you would signify your agreement with and acceptance of the terms set out in this letter by signing and returning to us the enclosed copy of this letter. 


Yours
faithfully,

RIO TINTO AMERICA INC. 



	/s/ [SIGNATURE ILLEGIBLE]
Authorised Signatory	 	 





We
agree with and accept the terms set out in your letter of 14 June 1999 to us of which the above is a true copy. 



	Date:	 	June 28, 1999
	 	/s/ [SIGNATURE ILLEGIBLE]
 V.P. & CFO

Kennecott Energy & Coal Company





















  RIO

TINTO  



	 	 	Patricia A. Britton

Vice President and Chief Legal Officer





28 February
2003 


Mr. Bret
K. Clayton

President and Chief Executive Officer

Kennecott Energy and Coal Company

505 South Gillette Avenue

Caller Box 3009

Gillette WY 82717-3009



Dear
Mr. Clayton, 


I
refer to the letter agreement dated 24 June 1998, as amended with effect from 1 April 1999, between Kennecott Energy and Coal Company ("KECC") and Rio Tinto America Inc.
("RTA"), whereby RTA agreed to make available to KECC a credit facility of up to $800,000,000 at any time outstanding on the terms set forth therein (the "Letter Agreement"). 



Following
recent discussions, KECC and RTA have agreed the rate of interest payable on borrowings under the credit facility shall be changed. Accordingly, with effect from 1 October 2002, the
words "a margin of two point one zero percent (2.10%)" shall be deleted from the Letter Agreement, and the words "a margin of three point six zero percent (3.60%)" substituted therefore. The Letter
Agreement shall continue in full force and effect, as amended, with effect from 1 October 2002, as set forth above. 


This
amending letter agreement shall be governed and construed in accordance with the laws of the state of New York. 



I
would be grateful if you would signify your agreement with and acceptance of the terms set forth in this amending letter agreement by signing at page two of the enclosed duplicate copy and returning
the same to me. 


Regards, 



	/s/ Patricia A. Britton
 Patricia A. Britton	 	 





Kennecott
Energy and Coal Company agrees with and accepts the terms set forth above in this amending letter agreement with respect to amendment of the 24 June 1998 credit facility between
Kennecott Energy and Coal Company and Rio Tinto America Inc. 



	

DATED:	
 	

3/3/03
	
 	

KENNECOTT ENERGY AND COAL COMPANY
	

 	
 	

 	
 	

By:	
 	

/s/  BRET K. CLAYTON      
 BRET K. CLAYTON
	 	 	 	 	Its:	 	President and Chief Executive Officer













QuickLinks



Exhibit 10.21